Drill Bits - Cobalt Numbered Drill Bits are for sale by Bisco Tool Supply. #21 Cobalt Numbered Drill Bits are USA made and manufactured to National Aerospace standard 907. Bisco's industrial quality cobalt drill bits are made of heat resistant cobalt and these USA made cobalt drills display a higher red hardness which permits speeds up to 30% greater than high speed steel drill bits. Cobalt drill bits are manufactured for drilling tough, high tensile materials like PH stainless steel, inconel and titanium. The #21 cobalt numbered drill bit has a .1590 decimal equivalent, 2-1/8 flute length, and 3-1/4 OAL. Call the sales staff at Bisco Tool toll free 1-866-247-2635 with any questions on drill bits or cobalt numbered drill bits.